1. Field of the Invention
Embodiments of the present invention relate to a test phantom for tomographic imaging. More particularly, embodiments of the present invention may be applied to breast tomosynthesis.
2. Description of the Prior Art
For many years it has been known, especially in mammography, to use test phantoms for testing performance levels of equipment. In one particular example, these test objects are in the form of a supporting structure on which a test slab in wax is placed, small structures are embedded in the test objects to model, for example, micro-calcifications, fibrous structures or tumours.
These test phantoms, for example those marketed by CIRS (CIRS 015) or Gammex (Gammex 156), are given particular use under the ACR accreditation program (“American College of Radiology”).
Test phantoms are also known to be used in mammography to calibrate or evaluate artefacts, and are in the form of fully homogeneous slabs.
More recently, phantoms for breast mammography have also been proposed in which each phantom has a substrate in a material, in radiological terms, that is equivalent to the adipose envelope of the breast, this substrate being conformed to imitate the shape of the breast. Two types of substrates are provided, ring phantoms either in the shape of a compressed breast or in the form of a pendant breast.
At the center of each substrate is a cubic housing intended to receive assemblies of elementary structures of slab or cube type. Inserts intended to reproduce micro-calcifications or fibres are embedded in these elementary structures. Provision is also made so that elementary cubes devoid of any insert can be used to test the observer.
It is also desirable, notably in mammography, to be able to detect not only micro-calcifications, fibrous structures or tumours, but also to be able to evaluate the glandularity of tissues, i.e. the percentage of fibroglandular tissue contained in total fibroglandular and adipose tissue.
Methods for the digital processing of images have been proposed in this respect, but are not yet fully satisfactory. In particular, the methods only allow binary classification between dense tissue and fatty tissue, but fail to give full satisfaction.
For tomography or tomosynthesis, there is also a need for tools that can be used to assess, notably quantitatively, the rendering of images produced by the tomographic or tomosynthesis device. For mammography, in particular, the low number of acquired projections and limited angle views can lead to bias with respect to voxel values which, for practitioners, does not contribute to facilitating evaluation of the glandularity of mammary tissue in available images.